1. Technical Field
The present invention relates to a Raman spectroscopic apparatus, a Raman spectroscopic method, and an electronic apparatus.
2. Related Art
In recent years, the demand for a sensor chip (optical device) used for medical diagnosis, beverage and food inspection, and other purposes has been increasing, and the development of a highly sensitive, compact sensor chip has been desired. To meet the demand, sensor chips of a variety of types including a sensor chip using an electrochemical approach have been studied. Among them, a sensor chip using spectroscopic analysis based on surface plasmon resonance (SPR), in particular, surface enhanced Raman scattering (SERS) has received increasing attention for a variety of reasons. For example, such a sensor chip can be an integrated chip, can be manufactured at low cost, and can be used in any measurement environment.
Surface plasmon is a vibration mode of an electron wave that is coupled to light under certain surface-specific boundary conditions. To excite surface plasmon, there are a method in which a diffraction grating engraved on a metal surface is used to couple light and plasmon to each other and a method in which an evanescent wave is used. An example of a sensor chip using SPR is formed of a total reflection prism and a metal film that is formed on a surface of the prism and comes into contact with a target substance. The thus configured sensor chip detects whether or not a target substance has been adsorbed, for example, whether or not an antigen in an antigen-antibody reaction has been adsorbed.
There is propagating surface plasmon present on a metal surface, whereas there is localized surface plasmon present on a metal fine particle. It is understood that when the localized surface plasmon, that is, surface plasmon localized on a metal microstructure of a surface is excited, a significantly enhanced electric field is induced.
It is further understood that when an enhanced electric field formed by localized surface plasmon resonance (LSPR) using metal nano-particles is irradiated with Raman scattered light, a surface enhanced Raman scattering phenomenon enhances the Raman scattered light, and a highly sensitive sensor (detection device) has been proposed. Using the principle described above allows detection of trace quantities of a variety of substances.
For example, JP-A-2013-96939 describes a Raman spectroscopic apparatus including a sensor chip in which metal particles made of Ag or Au are periodically arranged.
However, the Raman spectroscopic apparatus described in JP-A-2013-96939, which has a trap film, cannot detect every target substance in a highly sensitive manner. Further, for example, a Raman spectroscopic apparatus including a sensor chip (optical device) in which metal particles made of Ag are periodically arranged can detect a molecule containing an N atom having an unpaired electron, such as pyridine and adenine, in a highly sensitive manner because Ag tends to chemically adsorb such a molecule but cannot detect a molecule not containing an N atom, such as acetone and ethanol, in a highly sensitive manner because Ag does not tend to chemically adsorb such a molecule.